Ion gyroscale fluctuation measurement with microwave imaging reflectometer on KSTAR

Area of Science:

• Plasma Physics
• Fusion Energy Research
• Fluid Dynamics

Background:

• Tokamak plasmas exhibit complex turbulent fluctuations.
• Understanding these fluctuations is crucial for achieving stable fusion conditions.

Purpose of the Study:

• To measure ion gyroscale turbulent fluctuations in neutral beam injected L-mode plasmas.
• To identify the primary cause of these fluctuations in fast-rotating tokamak plasmas.

Main Methods:

• Utilized multichannel microwave imaging reflectometry to measure turbulence.
• Employed linear and nonlinear gyrokinetic simulations for comparison.
• Deduced poloidal wavenumbers from measured frequencies and rotation velocities.

Main Results:

• Measured poloidal wavenumbers of ion gyroscale turbulent fluctuations at kθ ∼ 3 cm⁻¹.
• Gyrokinetic simulations predicted unstable modes consistent with measurements (kθρs ∼ 0.4).
• Experimental frequencies closely matched simulation intrinsic mode frequencies, dominated by E × B flow.

Conclusions:

• The E × B flow velocity is the dominant factor in measured turbulence frequencies.
• Findings provide critical insights into plasma turbulence control in fusion devices.
• Experimental and simulation data show strong agreement, validating the models used.